This invention relates generally to photoprinting and, more specifically, to apparatus and method for sequential positioning of photoprinting plates with respect to a resist covered web so that a single photoprinting plate can be used to form multiple images on the resist covered web with the multiple images forming a single continuous image.
The concept of precisely alignment photoprinting plates with each other when the photoprinting plates are located on opposite sides of a resist covered web is shown and described in U.S. Pat. No. 5,814,826. Typically, one of the photoprinting plates is fixed and the other is positionable with respect to the fixed photoprinting plate by a set of drive motors. The drive motors are controlled by a compartor that determines the necessary positioning required to place the two photoprinting plates into alignment with each other. In the U.S. Pat. No. 5,814,826 a laser emitting diode is used to assist in alignment of the two photoprinting plates with each other. This method of alignment works well for accurately positioning photoprinting plates, which are located on opposite sides of a resist covered web, in alignment with each other so that when the images on the photoprinting plates are projected onto the resist covered web the images on opposite sides of the web are in precise registration with each other. Typically, aperture or shadow masks for use in cathode ray tubes and the like require registration of the images on opposite side of the web to be on the order of 0.0001 inch or less. While the alignment of photoprinting plates on opposite sides of the metal web with one another can be obtained it is more difficult to form image in lateral registration with one another. By lateral registration of images it is understood to mean two sequentially formed images in a resist covered web are located in precise registration with one another so that the two lateral images, which are produced at different times, appear as a single continuous image. By forming sequential lateral images in lateral registration one can form images on the metal web that are larger than the images that can be carried on a single photoprinting plate.
One of the difficulties with using a photoprinting plate to form multiple lateral images is the difficulty in accurately repositioning the photoprinting plates with respect to the first image so that one can project a second image onto the resist covered web which is in lateral registration with the first image. Oftentimes, sequentially formed images usually contain gaps or discontinuous images since the photoprinting plates can not be accurately positioned with respect to the first image. As a result, the images formed in the resist covered web have been generally limited by the size of the photoprinting plate. That is, if the photoprinting plate has a width of 30xe2x80x3 the image projected from the photoprinting plate onto the resist covered web needs to be less than 30xe2x80x3 in order to obtain the necessary precision in the projected image. One of the problem with large photoprinting plates, which are typically made from glass, is that they are both expensive to make and subject to breakage. Thus a need exists for maintaining smaller photoprinting plates while having the ability to form large images.
Consequently, because of the difficulty in accurately positioning of the photoprinting plates so that a second image can be combined with a first image to produce a larger composite image the size of the images have been generally limited by the size of the photoprinting plate. With the present invention, the size of the usable image formed on the resist covered metal web can be larger than the photoprinting plate. That is, by use of an alignment method and apparatus one can not only precisely align two photoprinting plates with respect to one another but one can use the photoprinting plates to form a first printed image and then by being able to precisely reposition the photoprinting plates with respect to the web one can print a second image which is in register with the first image. To provide for sequential formation of images in register one uses an on-the-go formation of a set of web alignment holes in the resist covered web. The web alignment holes, which are formed in the web by a punch or the like are used to accurately position the web proximate the reference markings on the photoprinting plate so that one can print sequential images in precise registration with each other.